ProQR Therapeutics ($PRQR) has pushed back the date on which it expects to deliver data from its cystic fibrosis clinical trials. The delay means it may be late 2016 before ProQR presents data on its challenger to Vertex Pharmaceuticals' ($VRTX) grip on the cystic fibrosis market.

Leiden, the Netherlands-based ProQR blamed the setback on slower than expected enrollment, which it sees as a consequence of stringent inclusion/exclusion criteria and an uptick in the number of studies competing for the same pool of potential trial participants. The upshot for ProQR and the investors who bankrolled its $97.5 million (€91.9 million) IPO is that top-line data from a pair of trials of cystic fibrosis drug QR-010 are now due for release in mid- to late 2016. Shares in ProQR fell by as much as 30% in the hours following the publication of the revised timeline.

The setback is the latest in a string of slips in the execution of the clinical development program. When ProQR filed to go public in September 2014, it told investors to expect data from a proof-of-concept study in the third quarter of 2015, with the readout from a Phase Ib trial following a few months later. By the time ProQR published its annual report in April of this year, the target for both trials had moved. At that time, ProQR was guiding that it would release data from both studies in the second half of 2015 or first half of 2016.

Now, even the most negative reading of this earlier timeline looks optimistic. ProQR is working with 22 sites to enroll patients in the Phase Ib dose-escalation study. The other trial, a proof-of-concept nasal potential difference (NPD) study, has activated a handful of sites. Collectively, the centers are struggling to get patients into the trial. ProQR is trying to improve the situation. "Our teams have taken a number of steps to accelerate enrollment without compromising on quality," ProQR CEO and co-founder Daniel de Boer said in a statement.

De Boer spent much of his career in IT, but the list of people behind ProQR includes some notable names in biotech circles. Henri Teemer and Dinko Valerio, the former CEOs of Genzyme and Crucell, respectively, co-founded the company with de Boer and Gerard Platenburg. Teemer and Valerio now serve on the supervisory board, while Platenburg, a founder of Prosensa, serves as chief innovation officer.